Conventionally, by splitting a permanent magnet embedded in a rotor core of a rotating electrical machine by cleaving so as to reduce its surface area, an eddy current generated by fluctuation in an acting magnetic field has been reduced and heat generation of the permanent magnet caused by the eddy current has been suppressed, thereby preventing irreversible thermal demagnetization.
In JP2009-142081A, a permanent magnet in which a notch which becomes a target of cleaving is provided in advance is inserted into a container having an inner hollow dimension and an inner hollow shape of a rotor slot and filled with a resin, then the permanent magnet is cleft into magnet pieces in the container and the resin is made to infiltrate between the magnet pieces at the same time as the cleaving.